Swimming depth and thermal history of individual Atlantic salmon (Salmo salar L.) in production cages under different ambient temperature conditions

Salmon production cages at sites with a pronounced thermal stratification give individual fish an opportunity to choose their thermal environment. The behavioural responses of individual salmon to such stratification, however, are poorly documented. Information about spatial distributions and temperature experience of individual Atlantic salmon (initial weight 1.5 kg) was gathered over a period of 4 months (mid-August to early-December) using data storage tags. Fish were stocked at normal or high densities in triplicate 2000 m³ production cages at 5.6–14.5 (ND) or 15.7–32.1 (HD) kg m^− 3, and valid data were collected for 12 ND and 11 HD salmon. There were large inter- and intra-individual variations in swimming depth, with indications that the salmon performed behavioural thermoregulation in an attempt to maintain body temperature within the range of 8–20 °C. Stocking density influenced the average swimming depth and body temperature, indicating competition for preferred thermal space in periods of unfavourably high temperature (towards 20 °C) in large parts of the cage volume. Analysis of temporal behavioural patterns demonstrated a higher variability during day than night and that 60 to 70% of the individuals displayed cyclic diel patterns in either swimming depth or body temperature in at least one out of three sub-periods. The results are discussed in relation to bio-energetic and thermal stress theory and possible consequences for growth variation in salmon cages. Generally, this study suggests that individual swimming depth and body temperature is in part a response to available temperature interacting with stocking density and time of day, while some individual variation cannot be ascribed to the measured variables.     

Submerged light increases swimming depth and reduces fish density of Atlantic salmon Salmo salar L. in production cages

Artificial photoperiods that postpone sexual maturation and increase growth are now widely used in the Atlantic salmon Salmo salar L. farming industry. Few studies have been carried out to examine the effect of this treatment on fish behaviour and welfare in production cages. In this study, echo‐integration was used to observe the swimming depth and fish density of salmon in 20‐m‐deep production cages illuminated by lamps mounted above the water surface (SURF) or submerged in the cage (SUBS). From January to May, SUBS swam at a greater depth (5–11 m) than SURF (1–3 m) at night. SURF descended and SUBS ascended at dawn, but SUBS were still swimming at greater depth than SURF during the day from January to March. The difference in swimming depth resulted in SURF swimming at a median fish density about twice as high as SUBS at night and up to five times the calculated fish density. SURF increased the utilization of the cage volume as the biomass increased, but fish swimming at the highest density did so at up to 20 times the calculated fish density. The results suggest that salmon position themselves in relation to the artificial light gradient to maintain schooling behaviour and that the use of submersible lights may be a precaution to secure the welfare of caged salmon.     

The prevalence of vertebral deformities is increased with higher egg incubation temperatures and triploidy in Atlantic salmon Salmo salar L.

Suboptimal egg incubation temperature is a risk factor for the development of skeletal deformities in teleosts. Triplicate diploid and triploid Atlantic salmon, Salmo salar L., egg batches were incubated at 6, 8 and 10 °C up until first feeding, whereupon fish were reared on a natural temperature before examination for externally visible skeletal deformities (jaw and spine) and radiographed for vertebral deformities and morphology at the parr stage. Increasing incubation temperatures and triploidy increased the number of fish showing one or more deformed vertebrae. Triploids had significantly higher mean vertebrae cranio‐caudal length (L) and dorsal‐ventral height (H) ratio at 6 and 10 °C than diploids, but triploidy had no effect on mean vertebrae centra area. Triploids demonstrated an increase in lower jaw deformities with increased incubation temperature, whereas jaw deformities were rare in diploids. Fish incubated at 10 °C had a significantly lower mean vertebral number than fish incubated at 6 °C, and triploids had lower mean vertebral numbers than diploids. Diploid fish with 58 vertebrae had a significantly higher mean vertebral centra area than fish with 59 vertebrae, but vertebral number did not affect the mean vertebral L/H ratio. The results are discussed with respect to the welfare and production of farmed salmonids.     

Assessment of “discreet” vertebral abnormalities, bone mineralization and bone compactness in farmed rainbow trout

The present study aimed to evaluate the importance of “discreet” vertebral abnormalities in normally-shaped rainbow trout in relation to vertebral bone condition in French fish farms. A total of 373 trout (262 ± 2 mm in total length) from 20 fish farms sampled were studied. The fish were radiographed and the axial skeleton examined for vertebral abnormalities. Vertebrae from the middle axial region (V32-38) were selected to evaluate vertebral bone condition. Bone mineralization (BM, %) was estimated by the ratio of ash and dry weight. Bone compactness (BC,%) was measured using Bone Profiler 3.23 images software on digitized radiographs of transverse sections (125 ± 10 μm). Statistical analyses were performed to test the relationships between the occurrence of vertebral abnormalities, and BM and BC. The occurrence of affected trout ranged from 0 to 55% depending on the farm. Trout displayed vertebrae with low BM (< 54.6%) and low BC (< 28.1%) in 40% and 55% of the farm, respectively. No relationships were observed between bone condition parameters (BM, BC) and the occurrence of vertebral abnormalities. These results could be explained by a wide and variable plastic response of bone characters (i.e., vertebral abnormalities, BM and BC) to the various rearing conditions in the fish farms sampled.     

Sustained exercise improves vertebral histomorphometry and modulates hormonal levels in rainbow trout

Abnormal compressions and fusions of vertebral bodies are frequently observed in reared rainbow trout and could result from chronic and unbearable muscle pressures acting on the axial skeleton during intensive growth. Sustained swimming at moderate speeds was shown to induce many positive effects on growth and swimming performances in salmonids, but yet little is known about its effects on vertebral remodeling processes and related hormonal regulation. Rainbow trout were subjected to three different swimming speeds (0, 1.0 and 1.5 body length (BL) s^− 1), starting one month after they were first fed (65 mm) and ending when they reached 260 mm in size (market-size of 275 g). At the end of the experiment, 20 trout were sampled in each lot (N = 60) and blood samples were taken. Vertebrae abnormalities were assessed by radiological examinations. Vertebrae from the middle axial region (V32–38) were selected to evaluate bone mineralization (BM) and total bone area (Tt-B.Ar.) on radiographed transverse sections (125 ± 10 μm). Assays were performed to evaluate mineral homeostasis (calcemia and phosphatemia), bone cell activities (alkaline phosphatase, ALP, and tartrate-resistant acid phosphatase, TRAP) and bone regulating hormones (calcitonin, CT and thyroid hormones, THs). Sustained exercise reduced the appearance of fused vertebrae, enhanced vertebral BM and decreased vertebral Tt-B.Ar., while it increased circulating CT and TH levels. No variations were observed on mineral homeostasis and bone cell activities. Increasing the swimming speed up to 1.5 BL s^− 1 had positive effects on the vertebral skeleton, and therefore, seems to be a suitable approach to prevent aggravation of vertebral abnormalities in juvenile trout. The changes observed in vertebral features are interpreted as a compromise between the necessity to mobilize vertebral mineral ions in response to various physiological demands and to maintain vertebral strength against mechanical constraints.     

Evaluation of partial water reuse systems used for Atlantic salmon smolt production at the White River National Fish Hatchery

Eight of the existing 9.1 m (30 ft) diameter circular culture tanks at the White River National Fish Hatchery in Bethel, Vermont, were retrofitted and plumbed into two 8000 L/min partial water reuse systems to help meet the region's need for Atlantic salmon (Salmo salar) smolt production. The partial reuse systems were designed to increase fish production on a limited but biosecure water resource, maintain excellent water quality, and provide more optimum swimming speeds for salmonids than those provided in traditional single-pass or serial-reuse raceways. The two systems were stocked with a total of 147,840 Atlantic salmon parr in May of 2005 (mean size 89 mm and 8.5 g/fish) and operated with 87–89% water reuse on a flow basis. By the time that the smolt were removed from the systems between March 28 to April 12, 2006, the salmon smolt had reached a mean size of 24 cm and 137 g and hatchery staff considered the quality of the salmon to be exceptional. Overall feed conversion was <1:1. The Cornell-type dual-drain circular culture tanks were found to be self-cleaning and provided mean water rotational velocities that ranged from a low of 0.034 m/s (0.2 body length per second) near the center of the tank to a high of 39 cm/s (2.2 body length per second) near the perimeter of the tank. The fish swam at approximately the same speed as the water rotated. System water quality data were collected in mid-September when the systems were operated at near full loading, i.e., 24 kg/m³ maximum density and 52.1 and 44.1 kg/day of feed in system A and system B, respectively. During this evaluation, afternoon water temperatures, as well as dissolved oxygen (O₂), carbon dioxide (CO₂), total ammonia nitrogen (TAN), and total suspended solids (TSS) concentrations that exited the culture tank's sidewall drains averaged 14.8 and 15.9 °C, of 7.9 and 8.2 mg/L (O₂), 4.0 and 3.2 mg/L (CO₂), 0.72 and 0.67 mg/L (TAN), and 0.52 and 0.13 mg/L (TSS), respectively, in system A and system B. Dissolved O₂ was fairly uniform across each culture tank. In addition, water temperature varied diurnally and seasonally in a distinct pattern that corresponded to water temperature fluctuations in the nearby river water, as planned. This work demonstrates that partial reuse systems are an effective alternative to traditional single-pass systems and serial-reuse raceway systems for culture of fish intended for endangered species restoration programs and supplementation programs such as salmon smolt.     

Physiological responses to continuous swimming in wild salmon (Salmo salar L.) parr and smolt

Wild salmon (Salmo salar) parr and smolt were forced to swim against constant flow (50 cm.s^–1) for 8 hours. Physiological properties describing the hormonal status, the energy metabolism and the ionic and osmotic balance of fish were measured from the fish prior to and at the end of the swimming test.Plasma cortisol levels were elevated in response to enforced swimming; the response of the smolt was clearly greater than that of the parr. Plasma thyroxine concentration increased in the parr but stayed at the initial level in the smolts. The parr consumed much of their coelomic fat, but the glycogen stores stayed nearly constant. The smolts had very low fat stores, and the glycogen stores were depleted in the test. The ionic and osmotic balance of the parr was stable in the test, but in smolts, the plasma Cl^–1 and osmotic concentrations decreased and muscle moisture increased.The results indicate that downstream migration smolts have markedly lower physiological capacity for continuous swimming than parr.     

Behavioural ecology at sea of Atlantic salmon (Salmo salar L.) kelts from a Newfoundland (Canada) river

For migratory fishes such as Atlantic salmon, temporal variation in the utilization of thermal and depth habitats in the marine environment is likely to occur at both broad and fine scales, reflecting both ecological and metabolic factors. To test this, we implanted 26 Atlantic salmon kelts (i.e., post‐spawners) descending Campbellton River, Newfoundland, with data storage tags that recorded date/time, internal and external temperatures, pressure, and light. The salmon that returned to Campbellton River after an average of 62 days at sea were consecutive spawning kelt. Detailed data were recovered from eight of these fish and revealed distinct patterns in their utilization of thermal and depth habitats. Water temperatures experienced over the period at sea showed a wide range for all fish (from <0 to nearly 20°C); however, there were two clear frequency modes; one at 6–7°C and the other at 11–12°C. The cooler mode was indicative of daytime profiles and the warmer mode of night‐time profiles. This corresponded with the depth profiles, which indicated that salmon dove more frequently below 5 m (mean ± SD = 23 ± 0.9 dives per day) and spent less time (approximately 18%) near the sea surface (<1 m) during the day than during the night (4 ± 0.4 dives per night; approximately 45% time <1 m). The diurnal pattern may be indicative of a reliance on vision for feeding at depth and the short duration of dives (<10 min) may be a strategy that allows salmon a metabolic advantage (e.g., swimming capacity) over their prey living constantly at depth in cool waters.     

Growth of Atlantic salmon (Salmo salar L.) in a variable diel temperature regime

In five experiments, Atlantic salmon (Salmo salar L.) parr were found to grow better under conditions of rhythmically alternating water temperature (P<0.031), than control groups reared under stable temperature conditions. The daily temperature sums for the experimental and the control groups were carefully equalized and monitored in all five experiments. The experimental group was reared in a rhythmically alternating temperature regime, of 10.0 h of high temperature (16.0°C) and 10.0 h of low temperature (10.0°C), the temperature adjustments being made during the 2 h between the periods of fixed temperature. The control group were reared in a relatively stable temperature regime (13.00–13.98°C). The growth rate of the fish reared under the varying temperature conditions was higher (mean for all five experiments 1.96% day⁻¹) than that for the salmon reared under stable conditions (1.85% day⁻¹).     

Effects of swimming speed and dissolved oxygen on geosmin depuration from market-size Atlantic salmon Salmo salar

Common off-flavor compounds, including geosmin (GSM) and 2-methylisoborneol (MIB), bioaccumulate in Atlantic salmon Salmo salar cultured in recirculating aquaculture systems (RAS) resulting in earthy and musty taints that are unacceptable to consumers. To remediate off-flavor from market-ready salmon, RAS facilities generally relocate fish to separate finishing systems where feed is withheld and makeup water with very low to nondetectable GSM and MIB levels is rapidly exchanged, a process known as depuration. Several procedural aspects that affect salmon metabolism and the associated rate of off-flavor elimination, however, have not been fully evaluated. To this end, a study was carried out to assess the effects of swimming speed and dissolved oxygen (DO) concentration on GSM levels in water and fish flesh during a 10-day depuration period. Atlantic salmon (5–8 kg) originally cultured in a semi-commercial-scale RAS (150 m³ tank) were exposed to a concentrated GSM bath before being transferred to 12 replicated partial reuse depuration systems (5.4 m³ total volume). Two swimming speeds (0.3 and 0.6 body lengths/sec) and two DO levels (90% and 100% O₂ saturation) were applied using a 2 × 2 factorial design (N = 3), and each system was operated with a 5-h hydraulic retention time, creating a water flushing to biomass ratio of 151 L/kg fish biomass/day. Geosmin was assessed at Days 0, 3, 6, and 10 in system water and salmon flesh. A borderline effect (P = 0.064; 0.068) of swimming speed was measured for water and fish, respectively, at Day 3, where slightly lower GSM was associated with low swimming speed (0.3 body lengths/sec); however, differences were not detected at Days 6 or 10 when salmon are commonly removed for slaughter. Overall, this research indicates that significant improvements in GSM depuration from RAS-produced Atlantic salmon are not expected when purging with swimming speeds and DO concentrations similar to those tested during this trial.     

A radiological study on the development of vertebral deformities in cultured Atlantic salmon (Salmo salar L.)

This study investigated the development of skeletal deformities in individually tagged Atlantic salmon (n = 805) from the parr stage (Sept 2001, 70 g mean ± 34 g S.D.) until 10 month after transfer to seawater (Feb 2003, 3040 g mean ± 1097 g S.D.). A subgroup of the total population (n = 129) was radiographed as parr (Feb 2002) and again 10 months after transfer to seawater (Feb 2003). Eight percent of the males matured sexually during their first autumn in sea (jack), and were excluded from further analysis. Based on an external examination of each fish (n = 773), 1.8% (n = 14) developed skeletal deformities (0.1% operculum deformities (n = 1), 0.4% jaw deformities (n = 3), 1.3% vertebral deformities (n = 10)) during the experiment. Based on evaluation of radiographs (n = 129), the prevalence of vertebral deformities was 7.0% (n = 9) at the parr stage, and 12.4% (n = 16) 10 months after transfer to seawater. From radiographs, longitudinally compressed vertebral bodies without intervertebral spaces were classified as ankylosis and compression, longitudinally compressed vertebral bodies with intervertebral spaces were classified as compressions, and dislocated vertebral bodies with a normal morphology and without intervertebral spaces were classified as ankylosis and dislocation. Of the fish that developed deformities during the experiment, 8 had ankylosis and compressions, 7 had compressions and 1 had ankylosis and dislocation. Ankylosis and compression developed in the region between vertebrae number 1 and 16, whereas compressions developed in the region between vertebrae number 13 and 49. Most of the individuals with compression 10 months after transfer to seawater had normal vertebral columns as parr, whereas all individuals with compression and ankylosis 10 months after transfer to seawater had deformed vertebral columns as parr.     

Case studies of spinal deformities in ornamental koi,Cyprinus carpio L.

This is a study of vertebral deformities in ornamental koi based on computed radiography and skeletons cleaned by dermestid beetles (Dermestes maculatus). All koi developed gradual onset of swimming abnormalities as adults. Extensive intervertebral osteophyte formation correlated with age of fish and was associated with hindquarter paresis in one koi. Vertebral compression and fusion were the most common spinal deformities occurring at multiple sites, similar to findings in other farmed fish. Site‐specific spinal deformities were thought to develop due to differences in swimming behaviour and rates of vertebral growth. One koi had offspring with spinal deformities. Spinal deformities are significant problems in both European and Australian food fish hatcheries. The heritability of vertebral deformities in farmed fish is reportedly low unless there is concurrent poor husbandry or nutritional deficiencies. The specific aetiologies for vertebral deformities in koi in this study could not be ascertained. Current knowledge on spinal deformities in the better studied European food fish species suggests multifactorial aetiologies. Future research should include prospective longitudinal studies of larger numbers of koi from hatch and consideration of all potential risk factors such as husbandry, nutrition, temperature, photoperiod and genetics.     

Analysis of sinking death using video images of the swimming performance of Pacific Bluefin tuna (Thunnus orientalis) larvae

In this study, we aimed to clarify the mechanism of sinking death during the larval stage of Pacific Bluefin tuna Thunnus orientalis by investigating the effects of swimming performance on sinking death, using a behavioral approach. Swimming performance was examined 3–9 days after hatching (DAH) under day and night light conditions in cuboid experimental tanks. Swimming behavior variables such as swimming speed and swimming angle were measured under both light conditions. Larvae in the daytime experiment and larvae with inflated swim bladders at night were distributed on the surface layer of the water column. In contrast, larvae with uninflated swim bladders at night were frequently observed swimming vertically or sinking to the bottom of the tank. Larvae with inflated swim bladders at night were always distributed beneath the surface until the next morning (survival rates were 100 %). However, larvae with uninflated swim bladders at night swam upward repeatedly and later sank to the bottom of the tank (survival rates were 60 % and 38 % at 5 and 9 DAH, respectively). Larvae with uninflated swim bladders were not always able to maintain their swimming depth by swimming until the next morning. Additionally, their swimming speed and vertical swimming frequency (ratio) depended on the illumination and swim bladder conditions. Our findings show that larvae with uninflated swim bladders at night were associated with a higher risk of sinking death. The swimming energy capacity of Pacific Bluefin tuna larvae, which indicates the total amount of the energy that enables individuals to swim throughout the night without feeding, was found to be linked to sinking death.     

Establishing an upper level of intake for vitamin A in Atlantic salmon (Salmo salar L.) postsmolts

The vitamin A (VA) concentration in salmon aquaculture feeds is varying and may lead to sublethal adverse effects. In this study, 135 g Atlantic salmon postsmolts were given eight diets in duplicates with 6, 12, 26, 55, 82, 112, 360 and 749 mg retinol (ROL) kg⁻¹ for 116 days. Subsequently, fish given 6, 82 and 749 mg ROL kg⁻¹ were transferred to a common net pen and given a standard commercial diet for further 28 weeks. Feed conversion rate, liver functionality and markers of VA homoeostasis were not negatively affected by dietary VA level, but chronic high VA intakes led to adverse effects on growth and bone health. In plasma, there was an antagonistic effect of dietary ROL on circulating 1,25 (OH)₂ vitamin D₃ (calcitriol). Moreover, a dose–response of VA on craniofacial deformities, condition factor and vertebral morphometry and mechanical strength was observed. Vertebral deformities were observed after 28 weeks on a standard diet and not immediately after the 116 days on the experimental diet. Elevated VA is a risk factor for bone deformities, and the dietary intake of VA should not exceed 37 mg ROL kg⁻¹ body weight day⁻¹ in Atlantic salmon postsmolts.     

Design, loading, and water quality in recirculating systems for Atlantic Salmon (Salmo salar) at the USDA ARS National Cold Water Marine Aquaculture Center (Franklin, Maine)

The Northeastern U.S. has the ideal location and unique opportunity to be a leader in cold water marine finfish aquaculture. However, problems and regulations on environmental issues, mandatory stocking of 100% native North American salmon, and disease have impacted economic viability of the U.S. salmon industry. In response to these problems, the USDA ARS developed the National Cold Water Marine Aquaculture Center (NCWMAC) in Franklin, Maine. The NCWMAC is adjacent to the University of Maine Center for Cooperative Aquaculture Research on the shore of Taunton Bay and shares essential infrastructure to maximize efficiency. Facilities are used to conduct research on Atlantic salmon and other cold water marine finfish species. The initial research focus for the Franklin location is to develop a comprehensive Atlantic salmon breeding program from native North American fish stocks leading to the development and release of genetically improved salmon to commercial producers. The Franklin location has unique ground water resources to supply freshwater, brackish water, salt water or filtered seawater to fish culture tanks. Research facilities include office space, primary and secondary hygiene rooms, and research tank bays for culturing 200+ Atlantic salmon families with incubation, parr, smolt, on-grow, and broodstock tanks. Tank sizes are 0.14 m³ for parr, 9 m³ for smolts, and 36, 46 and 90 m³ for subadults and broodfish. Culture tanks are equipped with recirculating systems utilizing biological (fluidized sand) filtration, carbon dioxide stripping, supplemental oxygenation and ozonation, and ultraviolet sterilization. Water from the research facility discharges into a wastewater treatment building and passes through micro-screen drum filtration, an inclined traveling belt screen to exclude all eggs or fish from the discharge, and UV irradiation to disinfect the water. The facility was completed in June 2007, and all water used in the facility has been from groundwater sources. Mean facility discharge has been approximately 0.50 m³/min (130 gpm). The facility was designed for stocking densities of 20–47 kg/m³ and a maximum biomass of 26,000 kg. The maximum system density obtained from June 2007 through January 2008 has approached 40 kg/m³, maximum facility biomass was 11,021 kg, water exchange rates have typically been 2–3% of the recirculating system flow rate, and tank temperatures have ranged from a high of 15.4 °C in July to a low of 6.6 °C in January 2008 without supplemental heating or cooling.     

Growth rates and survival of western rock lobster (Panulirus cygnus) at two temperatures (ambient and 23 °C) and two feeding frequencies

Wild caught post-pueruli, year one and year two post settlement juvenile western rock lobster, Panulirus cygnus, were held at ambient temperatures (15.6 °C to 23.1 °C; mean 19.0 ± 0.07 °C) or at 23 °C, and fed the same ration of a formulated pellet diet either once per night, or 3 times per night, over 12 months, to determine whether elevated temperatures and multiple feeds per night would stimulate growth through increased metabolism and feed utilisation without significant negative impacts on survival. Survival of post-pueruli (mean 63%) did not differ between ambient and 23 °C. Survival of year 1 and 2 juveniles was higher at ambient temperatures (p < 0.01 ambient: year 1 juveniles, 68%; year 2 juveniles, 88%; 23 °C: 57% and 74%, respectively). Feeding frequency did not affect survival of post-pueruli and year 2 juveniles (mean 63%, 81% respectively), but survival was 9% higher for year 1 juveniles fed three times per night (58% versus 67%; p < 0.01). All lobsters grew faster at 23 °C than at ambient temperatures (p < 0.05), with the growth of post-pueruli almost doubled at 23 °C (weight gain at 23 °C versus ambient: post-pueruli, 18 438 % versus 9 915 %; year 1 juveniles 259% versus 165%; year 2 juveniles 23% versus 21%). Feed frequency did not influence the growth of year 1 and 2 juveniles. However, there was an interaction effect of temperature and feed frequency on post-pueruli where weight and carapace length were significantly higher at ambient temperatures when post-pueruli were fed three times a day, whereas at 23 °C weight and carapace length were significantly greater when fed once per day (p < 0.05). Feed intake (g pellet dry matter lobster^− 1 day^− 1) of pellet was higher at 23 °C for all lobsters (p < 0.05), but was the same between lobsters fed 3 times per night versus once per night. This study has shown that increasing temperatures to 23 °C significantly improved the growth of P. cygnus post-pueruli without any adverse effects on survival. The faster growth rates exhibited by year 1 and 2 juveniles at 23 °C may potentially offset their lower survival by significantly reducing culture period. There is no benefit of feeding P. cygnus multiple times at night in terms of growth and survival. The implications for P. cygnus culture are that temperatures should be maintained close to 23 °C during the entire growout period, with due care taken to minimise mortalities through adequate provision of food and shelter. Feeding P. cygnus once daily to excess just prior to dusk to co-incide with nocturnal feeding behaviour is recommended.     

Fine‐scale movement ecology of a freshwater top predator,Eurasian perch (Perca fluviatilis), in response to the abiotic environment over the course of a year

Fine‐scale underwater telemetry affords an unprecedented opportunity to understand how aquatic animals respond to environmental changes. We investigated the movement patterns of an aquatic top predator, Eurasian perch (Perca fluviatilis), using a three‐dimensional acoustic telemetry system installed in Kleiner Döllnsee (25 ha), a small, shallow, mesotrophic natural lake. Adult piscivorous perch (N = 16) were tagged and tracked in the whole lake at a minimum of 9‐s intervals over the course of one year. Perch increased swimming activity with higher water temperature and light intensity. Air pressure, wind speed and lunar phase also explained perch movements, but the effects were substantially smaller compared to temperature and light. Perch showed a strong diel pattern in activity, with farther swimming distances and larger activity spaces during the daytime, compared to the night‐time. To investigate the influence of prey distribution, we sampled the prey fish in both littoral and pelagic zones in both day and night monthly using gill nets. We found that the prey fish underwent diel horizontal migration, using the littoral zone during the day and the pelagic zone during the night. However, perch showed the opposite patterns, suggesting either that the prey fish avoided predation risk or that the horizontal diel migration of perch was driven by other mechanisms. Our results collectively suggest that the movement ecology of piscivorous perch is mainly governed by a foraging motivation as a function of abiotic variables, especially temperature and light.     

Osteological development and deformities in hatchery‐reared longtooth grouper (Epinephelus bruneus): Vertebral column,dorsal‐fin supports and caudal‐fin skeleton

Skeletal deformities are one of the serious problems in hatchery‐reared longtooth grouper (Epinephelus bruneus). In this study, seed production of longtooth grouper was carried out in four large hatchery‐grade tanks. Osteological development of the vertebral column, caudal‐fin skeleton and dorsal‐fin supports in larvae and juveniles was described. The vertebral ontogeny started at 4.8 mm total length (TL) with the formation of neural spines 2 and 3, and the vertebral centra began forming at 5.3 mm TL. By 16 mm TL, all vertebral bony elements were formed except for the dorsal ribs. The onsets of the ontogeny of the caudal‐fin skeleton and dorsal‐fin supports occurred at approximately 5.1 mm and 3.9 mm TL, respectively, and the completion of these bony elements occurred at approximately 20 mm TL. The incidence of deformity was examined; some type of deformity was observed in 57%–68% of the specimens. These deformities mainly occurred as three types: lordosis, around vertebrae 1–5; saddleback‐like syndrome, around vertebrae 7–11; and vertebrae fusion, around vertebrae 22–24. The incidence of prehaemal lordosis was significantly higher among individuals with an uninflated swim bladder than among those with an inflated swim bladder.     

Active metabolism in larval and juvenile fish: ontogenetic changes,effect of water temperature and fasting

Oxygen consumption, ammonia excretion and fish swimming speed were measured in fish induced to swim by optomotor reaction in a circular metabolism chamber. The relationship between the swimming speed and fish metabolism described by exponential equations allowed the extrapolation to the standard metabolism, i.e. at zero swimming speed. The partitioning of the catabolised protein in the energy supply was estimated based on AQ (volume of ammonia/ volume of oxygen) values. Weight specific standard metabolism, as expressed by the ammonia excretion rate, decreased by one order of magnitude in coregonids as the fish grew from 20 to 780 mg body weight. The slope of the relationship between oxygen uptake and swimming speed decreased in coregonid ontogenesis. In salmon, after 12 days of fasting 28% of energy used was derived from protein, whilst coregonid juveniles utilized mostly lipid. Active swimming in fasted juveniles of coregonid, as well as in salmon, led to the accelerated utilization of protein as a source of energy, based on AQ coefficients. In juveniles acclimated to a range of water temperatures from 14 to 26°C, the changes in standard or active metabolic rate (expressed as oxygen uptake or ammonia excretion) were described by Q₁₀ coefficients. They were generally higher for the ammonia excretion rate than for the oxygen uptake rate and for active metabolism than for standard metabolism. Utilization of protein as energy for swimming differed significantly between the species, being in general one order of magnitude higher in coregonids than in salmon. The use of protein for swimming activity tended to decrease during coregonid ontogenesis.     

Osmoregulation in the mudskipper,Boleophthalmus boddaerti I. Responses of branchial cation activated and anion stimulated adenosine triphosphatases to changes in salinity

The mudskipperB. boddaerti, was able to survive in waters of intermediate salinities (4–27). Fish submerged in dechlorinated tap water suffered 60% mortality by the fifth day while 60% of those in 100% sea-water (sw) died after the third day of exposure. After being submerged in 50% or 80% sw for 7 days, the plasma osmolality, plasma Na⁺ and Cl^– concentrations and the branchial Na⁺ and K⁺ activated adenosine triphosphatase (Na⁺,K⁺-ATPase) activity were significantly higher than those of fish submerged in 10% sw for the same period. However, the activities of the branchial HCO₃ ^– and Cl^– stimulated adenosine triphosphatase (HCO₃ ^–,Cl^–-ATPase) and carbonic anhydrase of the latter fish were significantly greater than those of the former. Such correlation suggests that Na⁺,K⁺-ATPase is important for hyperosmotic adaptation in this fish while HCO₃ ^–-Cl^–-ATPase and carbonic anhydrase may be involved in hypoosmotic survival.